The present invention belongs to the machine tools industry and mainly to precision machine tool manufacture. More particularly, the invention relates to an improved spindle unit for a machine tool.
One of the main tendencies in the modern industry of machine tools is the essential and constant growing of a spindle""s maximal speed, especially in milling machine centers. The main problem is the contradiction between the spindle""s speed range, its stiffness, and its life time. As a spindle""s maximal speed becomes higher, its stiffness is lower. Thus, it is less suitable for roughing operations in the low speed range. The usage of high speed spindles for roughing will essentially reduce the roughing productivity and the spindle""s life time. The present invention addresses and solves this contradiction.
Accordingly, it is an object of the present invention to provide a spindle unit capable of working in a low speed powerful roughing regime and in a medium and high speed precision semi-finishing and finishing regime.
The foregoing object is attained by the spindle unit of the present invention.
In accordance with the present invention, a spindle unit has a body, a shaft placed into the body, and journal bearings between the body and the shaft. At least one journal-thrust ball bearing assembly is placed between the body and the shaft. A cylinder, which is operated either hydraulically or pneumatically, is provided to move the shaft in an axial direction. Further, a pad is placed on at least one side of the cylinder and enables the spindle to work as a fully restricted spindle with and without additional ball bearing support.
Other details of the spindle unit of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawing, in which like reference numerals depict like elements.